Process of manufacturing potassium tetraborate and sodium tetraborate



Patented Dec. 7, 1948 UNITED:

110 class 01 5M 55 5 5 A merdmss m 1A sonm eleme- Frank Heoderson Mas, was, Quit des n r to American Pfi ash & Chemical Conmpation,

f 5 5 55 n ne Gent.

This invention r l vtes wrin potassium tetmhomte; K BsOrAHzQ nd id nta ly sodlumw etrahomte, memo-101E120. Re ere ce s made tophe 101mm a ents and. app i ations covemngthe s me or re atedw subm matte which a e "e pendinz with th amuse 1942: Ma ee wqzawss is ue mw- Pe ent 25 3 55 6-5 weed on i-epblf ee n [H5 54 507,239, meaocmper 22,1943; MW and s ar;

Patent N05. 2,395, 6 issjlied or} applicatjoo No. 5

55811263, fi e dc o a r'l i w; mean we 5. 4 5 5. No. 507,298, filed October 22,

ll t sq i but the the; u amts eont m soluble carbonates, 5 the of :the process as described henemwremam inusomtim and docnqtmntammatethe prodmtw Equatiom fl fll are' kearried out at temperatures and afi the high tjempeg at ures employled, the pqtassmm-tetraborate and soul m tetraborate termed; remaih iti*solaition.

wi e these compoonds 5m solgttog if a 5 mom's i D a a e 5 No Drawing Amputation January 22, 1944,

(Ch s:

new The fidna o ll ne eted a high t m e atn e-wQn 9 l neslw olu ions h t m: t s n; tetra tew $01-$2 a d a rabewt fleewnl fiz s s 5w rystall z mflmee mw 17m t e s ut n and se materials areallowed tolorysltallize as a mixture,

sgch amixture relatively worthless, I have; discovered, however, that it is possible to eonsum the etyst-lliaatiQnhfi these compounds separately (by ieoourse to supersaturation phenom-5 em; By cooling under eonqitions iavoraible to maintain potassium tetraborate in its supexsajt urlatedstagte and for q fys allizing sodium tetra- IponateQJl have diseoyeid that it is possible to crystallize a heavy on not sodium tetraborate, after when it possible. to ,efiect crystallization of thepotassium tetraborate compound as a subx5 itf r hbr te 5 5 5 5 55 uhmitewmp es m ess 01 ype ressed'by Equation III. Potassium 5 stantially" pure product, uncontaminated by' so pe ritahoyat e sod ipixilbicarbor iate are added o wclw m ther i wnta n ne s b e oal bonateop bicarbonate in solution, and the mixture is boned warmers CO2 from the added ingrediehtsgessentially as expressed by EquationIIIJ The eyeliofmother liquor may contain mle ctmtmeecbe(earbonate or bicarbonates) 5 or it may Ontatn as muoM as 1 8 percent weight er theliquor; when expressed as KHCOa. I have mun-d that combined 0Q; contents in the wells rfiothefliquors at,-sa$' 35(3 rangihg from 7*pez7o tK-HCOz-to 18 peideotKHQ'Qi; are entirely s tisifactory for the operation of my process; "qhlebriteflon er theqimitof allowable combined fioaoojnteptis the ultimate solubility-of saaium mbartonasegmemos; If this value be exceeded; said solitf phase wi-l-l precipitate with the tetraborate crop. "Though the process may be operated satisfactorily with .eycli c mother liquors containing less than 7 pepoent combined 5 592 "w ms d i e ave ro :1 m re WW-H21 condu t we teestiqe of que ibn ,1 get, fFthe whee-the mother liquors are-less-ac id"-+i V i nc du *9 t e :h seii o nprm ns quantities of "the basifw porate s '(KmQr and NagB O7) in the hot so! ions; as is indicatedlby Eguatibnl f anq as will be more specifically dis- {The process being, cyclic I may begin a: description of an example with a cold mothei' liquorfrom a previous baltc h, This liquor; tained no suspended solids, was somewhat warmer than 35 0., and showed, by analysis 11.8 per cent 05 341 P59; 59- 5 mm n 9- 5 sweet 5:35:9 s m s KHQQ; was

Z 55 new man This liquor, I added 590 pounds of potassium pentaboratep- K2B1oO1s.8H2O, and 255 pounds of I also "added 170- sodium bicarbonate, NaHCOs. pounds of water which water may, if convenient or desired, consist of suitable wash waters from? previous operations, or even entrainedwater. (inv part at least) carried by theadded raw-ma terials-for example, wet filter cakes. 'The raw material may be contaminated with borax, without harm to the present process,a s one of the functions of the process is toproduce and crystallize borax, prior to recovering a crop of The weight of the raw materials, K2B10O1a'8H2Ci U and NaI-ICO: is seen to be 845 pounds, and the able tobring about the crystallization of sodium tetraborate, NazBiOmlflHzO while holding the potassium tetraborate, K2B4O7AH2O, in solution, in a state of high supersaturation, the while.

After completing the crystallization of a crop of borax, I then induce crystallization of the highly supersaturated potassium tetraborate, and cause it'to precipitate as a crop of commercially pure Kano-1.41120.

NaI-ICOa content of the -,mixture is seen to be about percent-the K2B1 0O16.8H20 content '70 percent. Such a mixture may be produced by the process of my copending application, Serial No. 507,300, filed October 22, 1943, issued May 1,1945,- as United States, Letters Patent No. 2,374,877; said prior process'provid-es a very desirable source of rawmaterial for the process of the present application. When employing a mixture of K2B1oO1s.8I-I2O and NaHCOs, such as that resulting from the operation of the process of my aforesaid co'pending. application, it often happens that said mixture will notshow, by analysis, solely K2B1'0O1c8I-I2O and NaHCOs. If said mixture has beenwashed .for the displacement of impurities, or partially dried in handling, some of the 002 may have been lost (i, e, the reaction expressed by Equation III mayhav'e taken place, in part, atjleast), .and the resulting .raw material will therefore show (by analysis) some potassiumtetraborate-or, it might be calculated to be a mixture of. K2B10O1s.8H2O and NaaCOa with or without some NaHCOs. Except for'the loss of the C02,.Whi0h is a valuablecommodity, such decomposition taking place in the raw material is of little consequence; but proper allowance must be made both in the matter of weights. and in the amount of CO2 to be subsequently boiled ofi.

The mixture of cyclic mother liquor, water; and potassium pentaborate-sodium I bicarbonate is next heated and boiled, to drive ofl carbon dioxide. In this example, the-expulsion of about 135 pounds of CO2 served tocomplete the reaction expressed by .Equation' III, insofar as the added solid ingredients are concerned.v The heat- I The, hot solution is placed in a suitable cooler, fitted with means for imparting mild agitation to y the solution and also fitted with suitable heat ing and liberation of CO2 results in a clear, syrupy liquor, which is next cooled as specified below.

The carbon dioxide liberated by the boiling operations may, to advantage, be used for the prep-.

aration of further quantities of the K2B1oO1s.8I-I2O -NaI-ICO3 mixture by aforementioned process of my ..co-

pending application. Or, such liberated CO2 may be used for other purposes, as it is extremely pure.

The boiling operation carries but little water off with the CO2, and such water may be Such a mixtureis relatively worthless. j I, have found that the tetraborates of potassium and of sodium possess quite similar solubility Such cooling, if not conducted with transfer (cooli ng means such as cooling coils or the like. 'Vacuum cooling may be employed after the hot solution has been cooled by indirect coolers to 50-60" C. and such a combination is quite satisfactory, as, at the-intermediate temperature, the COz-partial-pres'sure of the pregnant liquor has become negligible, and at the same time, it has not yet begun to deposit borate crystals. To bring about preferential crystallization of borax from'the solution simultaneously supersaturated with respect to the two tetraborates; I conduct this first cooling step relatively=quickly-say over a-period of'two h'ours,*or so. Also, to encourage said selective borax crystallization, I add to the batch, at the'low temperature, a pound or so of borax rystals, as seed. While some agitation of the batch is desirable andnecessary during the cooling operations, I try toi avoid excessive,

or violent, agitation". I u

By socooling to 35C. over a period of a couple of hours, I precipitated a crop of borax. This crop when centrifuged and given a light wash (which washings were kept separate from the liquor) was computed to contain about 575 pounds of j nazmomionzo On a liquor-free "basis, an analysis showed it to contain-98'.5 percent NazBiO-xQlOI-IzO, the major impurity beinga little -K2B1oO16.8H2O. Such borax may be dried andflsold as an article of commerce, or it may be utilized'in the aforementioned processor my copending application, for the man ufacture of a crop 0fK2B1oO1s.8I-I2Q-NaI-ICO3, by reacting it with KCl and CO2.

It will be noted thatthis crop of borax was essentiallyfreeof any ad'rnixture with solid-phase K2B4O7.4H2O,1 despite the fact that the solution from which it was crystallized was highly supersaturated at735 C. with respectto said potassium salt. I have found that sometimes, such potassium tetraborate does succeed in crystallizing with the borax crop, This condition can be readily recognized even withoutassistance of an analyst. The crystalfom'isof the two tetraborates are entirely dissimilar, and the presence of very much K2B4O1AH2O inthe borax cropmay be quickly and easily recognized by means of a magnifying glass" or a low-powerrmicroscope; When such potassium tetraboratecrystallization does take place with the borax crop, (usually asthe result of interruptions of operations-allowing the cold batch to standq'too long before removing the borax) it can beeasily cured,,viz: The mixture is heated-slightly-say to 4501', 55 C. until the offending K2B4O 4HzO crystals disappear; then the cooling is repeated, and a pure borax crop removed.

'Idqii'or'froni at its. separation set was then position, as th caused to precipitate a proper commercially pure potassium tetraborate, KtB OMHm. accom plished this by adding some, say apound of IQBrOrAI-Izi)" crystals to the cold liquor. {The seeded liquor-was their agitated fora relatiye'ly long time, say 18 hours ormore: At theerid of such period, the temperature still being aboutfifi 0., I proceeded to remove by centrifuging, a crop of potassium tetraborate. "This crop was also washed. (The washings may be passed intothe end liquor, to supply a portion of the water needed in thefollowing cycle.) Weighing and computatime showed the recovered crystal crop to contain about 300 pounds of KzBrOrAI-Izfi). Analysis showed the liquor-free solids to contain about cropwas possibly due to; theminor concentrate ine effect induced. by the. abstraction of. water (of crystallization) bythe crystallizing n K2B40'L4H2O o y Likewise, I havefound that thefirst crystalliza,

tion of borax often fails togo entirely to completionleaying smallsupersaturation. values (with respect to NazB4Q7=l0HgO) in theliquor. It the small quantity of N3.2B4Q'7.10H2O, so crystallizing with. the KzBrOqAI-I O crop is undesirable. it may be circumvented in several ways. A small amount f. wa e w y h d to he i o after: remoring the borax cro.p-saidsmall dilutionbeing sufificientk to satisfy the residual supersaturation values with. respect to NazBrOqlOH O and/or sutficient to; compensate the water of crystallization of the crop of K2B40m4H2Q to be crystallized; Another method for preventing further, mi;no13, bqrax crystallization with the KzBrQrAHzO; crop is by conducting the KzBrOa-AHzO. crystallization at. a slightly higher temperature than-y the Naz BroiloHzQycrystallization. Based upon my .disco ery that NazBiOmlOHzO also has a strong tendenc toward supersaturation, especially at relatively low supersaturation concentrations, I am provided. with a. third method for circumventing said. minor difiiculty, when; desired; By this method, I takethe filtered or centrifuged liquor rom the borax crop, a it l t isay to 4QP-50," C.) to destroy any line boraxlseedL an again cool it to. the original low temperature (3.5 C. in. the above example) or even lower. Under suchconditions borax seemsto be reluctant to. again; establish itself as :a separate solid phase, which. phase iould a ct ast a. contaminantof the KZB4 7- QH 1 P a 1 'Ljh product of the; above example is satisface tory as. a commercially pure product. However, it may be rendere deyen purer-by simple recrys tallization. Such recrystallization is highly eflicient due (1), to thesmalll quantities of impurities present, and, (2) to the fact that end liquors, or bleed ofi from the-recrystallization procedure may be added to thepresent cycle, cameras wash" waters or as make-up during the addition of theseveral; reagentsorrawmaterials: Bysuch recrystallization, I hate; made; many hundreds oi pounds of KzBiOvAHzO of 995+ percent purity. 'l he mother liquor;- resulting from the-j separation of the commercial KzBrOvAH O crop was essential thesame, bothin weight, and ma -1 A o employed; atthe start \jotthis 'enample; and it maybe used to" conduct another cycle. Although it is cooled and agitated for many'hours at 0., I find that it does not moneqmubnum even under such conditions. That is to say, it maycontain K2B1o01s.8Ha0, KzBiOqLHzO and NazBm10H20 in quantities considerablyereater than would obtain were the agitationlwith seedine) continued at 35 Cgior several-Weeks. i

'Itshould also be understood that the liberation of-C0z by yirtueofthe boiling operations was not complete. The hot batch, high in the basic ingredijents, Na2B4Om10H2O and KzBiOrAI-EQ; was boiledonlyenough to liberate the quantity of C0; correspondin with the requirements of Reaction I II, Further boiling would naveliberatect more GQ-z from such hot, alkaline solutions.

"1 have found, if the cold mother liquor be reheated to the boilingpoint (before again adding more raw materials thereto) that further liberatiomOfiCOatzikes place witheyen greaterease. I make use or this phenomenon when itis desired to" reduce the combined CO2 content ('KHGOs eontentl ofl the cyclic mother liquor. I believe that such boiling of the mother liquor brings about a reaction betweenthe bicarbonate in solution, and thdKgBioOrtaBHzO in solution, as might be' 'e'xpressed bytheequation: (lVl zms o ssmo+cxncot mo; y a K2B i- H2Oi-6G0e At any-rate, I. havevfound'that if suoh re-boiled solutlonsagain be cooled, seeded and agitated for 1.8 hours or so, aiiurthercrap or potassium tetraboratemay be recovered. However, I seldom make it a practice to. recover such an increment of KeBtOriAHzO separately, as the raw materials may be added. to the i e-boiled solution; further CO2 boiled off fiifdeslredil, the borax 'cropremovtedxandliboth the yie1dcrop and the i ncrementwcrop of KzBiomfl zo recovered together;

Motherliquor forstarting the cycle can be prepared in a number of ways. Obviously, it might be prepared by purchasing the ingredients (1011 their equivalents) heretoiores'et forth to represenat. the-composition of said liquor. However; I prefieu to make it by reacting KiBmOrs-flfifnfl and NaHCQa The reactions: involved in; the past; preparation of a suitable mother liquor are expressed bya combination of: Equation I'H above; and the equation: i l

of) 21 Q m- H Q+IONQHCOB+ H Q= a a stamp carbona e used; in place or. at

- lo t-h n Q QRIQ H Q- s would boa ombine:

hi9 0.: H011 II 841 om ZKtBiqChtBHiUqg5Na203+36H2*=" 4KHCO3+5Na2B40n10HO PQ3 lie one nitr ti n con ucte on a al o ment sca e rlc a c d about 2100 P n d a suitable m her li uo ng pe ati s Qc t in m mantle-.51pe c n CO2; (e -pr ss as K GQs n solu ion, ath icll mg mannerr l firs eished out aq ant tr 0t KBmOw-BHQGD-NaHCDa new. m teri l quivalen to, 14:1 h un K Bw ic-fifi Qf nd 0 hound /M11003. Th terial' waSg laced in a tank, containin cold Water add d to the tan lus a oa ntrainmenfil in, th r w ma e ia about, 1600'poundsl tiQ Qi SOIYQ T IIQSQUQS a dit na 30 pound of NQ-HQQ; (45 s o "NaiCO'z could have been substituted),

which made the total (equivalent) NaHCOa addition 860 pounds. CO2 was continued, without appreciable loss of water, .until analysis showed the hot syrupy liquor to contain about 8.4 percent byweight of remaining C02, expressed as KHCOs. This represents about 135 pounds of CO2 remaining in the liquor. Based upon an intake of 860 pounds or NaHCOa, there was liberated 315 pounds of CO2, or. 70 percent of the total CO2 contained in the reagents. Had NazCOz been substituted for NaHCOs, entirely, the remaining CO (expressed as KHCOs) would have been the same, but the quantity of CO2 to be liberated would have been only about 90 pounds.

The liquor was then cooled, finally to C. But, due to the enormous crop of borax which would have precipitated, in a single crystallization, the cooling was conducted stepwise, over a long period. The first cooling was carried to 50 0., and a crop of borax removed; a second cooling carried the liquor to C., and a further crop of borax was removed. A final cooling at 35 C. accompanied by long agitation (several days) brought out the final borax crop, which was a rated at 35 C. with respect to the K2Bi0O16.8H2O

and K2B207.4H20, neither of these components could precipitate with the borax crop, despite long-time cooling employed. The resulting mother liquor contained about,11.24 per cent K20, about 3.41 per cent NazO and 15.261 percent B203. It also contained about 14.5 percent CO2 when expressed as KHCOs. It constituted a suitable mother liquor for starting a cyclic process.

The foregoing example of the preparation of a mother liquor also illustrated a principle of my invention, namely, that the addition of alkali (NazCOs or NaI-ICOs) in excess of the approximate ratio of 7OKzB1cO1a3I-I20-30NaI-ICO3 tends to build up the solutions with respect to CO2, expressed throughout this specification as the KHCOs content. This is desired when manufacturing a mother liquor, and is permissible as a fluctuating factor over rather wide limits during the operation of the established cycle. However, overall, on the average, cycle after cycle, the quantities of raw materials added to, and removed from, the established cycle must fulfill the requirements of Equation II or Equation III- minor corrections being made for liquor losses by spillage and entrainment. The process is extremely flexible, and may be operated between wide limits of KHCO3 contents, as well as wide limits of concentrations of the reacting raw materials. About the only limitation to the latter is the thickness or density of the sludge of borax produced during the cooling operations. Since all the reagents (within reasonable limits) dissolve readily at the boiling-off temperatures, there is no necessity for controlling the process at that point, save to ascertain that overall (cycle after cycle) as much CO2 is boiled on as is required by Equation II or III.

If it is elected to employ caustic soda with potassium pentaborate, as per Equation I, the process of my invention is quite similar, though even simpler. In such instance it is unnecessary to heat the solution to the boiling point--a temperature of C. C. is sufiicient, prior to beginning the steps of preferential crystallization, as hereinbefore described. As an example 0! Boiling for the liberation ofsuch operation, to 3150 pounds of end liquor at 35C., I add 500 pounds of liquid caustic (commercial NaOI-Isolution) containing 48 percent NaOI-I. I also add the washings from a previous batch, said washings containing about pounds of, water. There is also added to the batch 1175 pounds of potassium pentaborate, K2B1oO1s.8I-I2O, which dissolves completely at about 50 C. in the presence of said caustic soda. I then proceed to cool the solution to 35 C. with mild agitation, over a period of two or three hours, thereby precipitating a crop ofborax, which upon removal by centrifuging weighs about 1145 pounds, and is essentially pure, i. e., free of solid-phase contamination with any other salt, save a small amount, less than 1 percent, of potassium tetraborate.

'Accordingto the. principles set forth in the foregoing exposition, the liquor from which the borax has been crystallized, is still highly supersaturated with respect to K2B41O'L4I'I2O. Accordingly, I proceed to crystallize said potassium tetraborate, at the same35 C. temperature, by, the addition of some K2B4O7AH2O seed crystals, and the application of agitation for a period of 18 hours or so. About 610 pounds of K2B4O7AH2O as a commercially pure product may be recovered by centrifuging the resulting sludge. This, upon washing anddrying to remove the adhering water may be marketed as such or recrystallized to remove the one or two percent of contaminating borax. The end liquor may be returned for the further processing of potassium pentaborate with caustic soda. The end liquors usually contain from 3 to to 5- percent, by weight of K2B4O7.4H2O and of Na2B4O7.10I-I2O more, than would be expected from equilibrium solubility determinations. The end liquorproduced in the above example contained 7.94 percent K20, 2.10 percent NazO and 16.10 percent B2Oathe remainder being essentially water.

As in the examples wherein sodium carbonate or bicarbonate were used for reaction with the potassium pentaborate, exact proportioning of any given batch is not vitally important. The "hot liquor may contain considerable unreacted KzBroOmBHzO, so long as the concentration of said reagent does not exceed a value of about 10 percent in the cold (35 C.) end liquor.

The impurities most likely to occur with the several raw materials are sodium pentborate (or some equivalent acid sodium borate) and sodium chloride. The former reacts with the soda alkali (NaHCOs, etc.) to yield borax, which borax is removed with the main borax crop generated by the reaction between potassium pentaborate and the soda alkali. Also it can react with KHCOa to give KzBioOic and NaHCOa0bVi0us1y desirable products. Hence, save for the possible consumption of alkali, such impurity is of little consequence. The presence of NaCl is however, undesirable, as it reacts with the generated to give borax and X01. Borax so produced is cared for in the obvious manner, but the loss of the K2B40'L4H2O is undesirable. Also accumulation of KCl in the cyclic mother liquor cannot be alloweito continue indefinitely. If the chloride content (calculated as KCl) of the cold mother liquor approaches about 20 percent, by weight, it will reach its saturation point, and, if exceeded, will precipitate with the borax crop. However, I have found that the presence of KCl, per se, is not deleterious to the system and that considerable quantity of such compound may, to advantage,

of the present invention herein described is well adapted to carry out the objects of the process, it is to be understood that various modifications may be made, and this invention includes such modifications and changes as fall within the scope of the appended claims.

I claim:

1. A process of manufacturing potassium tetraborate tetrahydrate, which comprises heating and reacting potassium pentaborate and a sodium compound from the group consisting of hydroxide, carbonate and bicarbonate to form sodium and potassium tetraborate in solution, thereafter cooling the solution to a point sufficient to crystallize borax from the solution while the potassium tetraborate remains dissolved in the solution, removing the, crystallized borax from the solution, and thereafter inducing crystallization of the potassium tetraborate to cause it to precipitate as potassium tetraborate tetrahydrate K2B4O7AH2O.

2. A process of producing potassium tetraborate tetrahydrate (KzB4O7.4H2O), which comprises heating and reacting a mother liquor containing sodium and potassium borates and carbonates, potassium pentaborate and a sodium compound from the group consisting of hydroxide, carbonate and bicarbonate, together so as to form sodium and potassium tetraborate in solution, thereafter cooling such solution to a point suflicient to crystallize borax (NazBcOmlOHzO) from the solution while the potassium tetraborate remains dissolved in the solution, separating the crystallized borax from the solution, and thereafter inducing crystallization of the potassium tetraborate to cause it to precipitate as potassium tetraborate tetrahydrate (K2B4OL4H2O) 3. A process of producing potassium tetraborate tetrahydrate (K2B4O7AH2O), which comprises heating and reacting a mother liquor containing sodium and potassium borates and carbonates, potassium pentaborate and a sodium compound from the group consisting of hydroxidacarbonate and bicarbonate, together so as to form sodium and potassium tetraborate in solution, thereafter cooling such solution to a point suflicient to crystallize borax (Na2B4O'L10HzO) from the solution while the potassium tetraborate remains dissolved in the solution, separating the crystallized borax from the solution, thereafter inducing crystallization of the potassium tetraborate to cause it to precipitate as potassium tetraborate tetrahydrate (KzBrOvAHzO), and returning the remaining mother liquor to the first-mentioned operation.

4. A process of manufacturing potassium tetraborate tetrahydrate, which process comprises reacting potassium pentaborate and a sodium carbonate together in solution while heating the solution to drive off carbon dioxide, thereby forming a potassium tetraborate and sodium tetraborate in solution, thereafter cooling the solution to a point sumcient to crystallize and precipitate borax from the solution while the potassium tetraborate remains dissolved in the solution, removing the borax from the solution, and thereafter inducing crystallization of potassium tetraborate tetrahydrate.

5. A process of manufacturing potassium tetraborate tetrahydrate, which process comprises adding to the mother liquor, from a previous operation and containing carbonate, potassium pentaborate and a sodium compound from the group consisting of hydroxide, carbonate and bicarbonate, heating the same to drive off carbon dioxide while forming potassium tetraborate tetrahydrate in solution, cooling the solution to a point sufficient to first crystallize and precipitate borax only from the solution while the potassium tetraborate remains dissolved in the solution, separating the produced borax from the solution, and thereafter inducing crystallization of potassium tetraborate tetrahydrate.

6. A process ofmanufacturing potassium tetraborate tetrahydrate, which process comprises adding to the mother liquor containing sodium and potassium borates and carbonates, from a previous operation, potassium pentaborate and a sodium compound from the group consisting of hydroxide, carbonate and bicarbonate, heating the same to drive off carbon dioxide while forming potassium tetraborate tetrahydrate in solution, cooling the solution to a point sufficient to first crystallize and precipitate borax only from the solution while the potassium tetraborate remains dissolved in the solution, separating the produced borax from the solution, and thereafter inducing crystallization of potassium tetraborate tetrahydrate, and returning the mother liquor from said last crystallization to the first operation.

'7. A process of manufacturing potassium tetraborate tetrahydrate, which process comprises adding potassium pentaborate and sodium bicar bonate to a mother liquor from a previous similar operation, heating the same to evolve carbon dioxide and form sodium and potassium tetrabor-, ate in solution, thereafter cooling the solution to a point suflicient to crystallize first borax only from the solution while the potassium tetraborate remains dissolved in the solution, separating the precipitated borax from the solution, thereafter inducing crystallization of potassium tetraborate tetrahydrate, removing the precipitate from the mother liquor, and returning the mother liquor to the first operation.

8. A process of manufacturing potassium tetraborate tetrahydrate, which comprises adding potassium pentaborate and a sodium compound from the group consisting of hydroxide, carbonate and bicarbonate, to a mother liquor containing between 7 and 18% of potassium bicarbonate, heating the same to evolve carbon dioxide from the solution and form sodium and potassium tetraborates in solution, cooling the solution to a point suflicient to first precipitate borax only while the potassium tetraborate remains dissolved in the solution, removing the borax from the solution, and thereafter inducing crystallization of potassium tetraborate tetrahydrate, removing such latter precipitate from the mother liquor, and returning such mother liquor to the first operation.

FRANK HENDERSON MAY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

